Several hundred carcasses of brown pelicans oiled by the BP blowout were recovered, but the death toll may be higher by a large multiple.

Almost from the start, wildlife advocates described the Deepwater Horizon oil spill as a war on the Gulf ecosystem. Few quibbled with that analogy as a record 210 million gallons spewed into the Gulf just 50 miles from one of the world’s most productive coastal estuaries.

Yet four years later, wildlife workers, especially those concerned about birds, are skeptical of one metric commonly used to assess wars of any kind: the official body count.

But wildlife specialists say those numbers are likely low by a factor of at least 10 — and no one should think the worst is over for the pelicans and a host of other less heralded bird species in the northern Gulf.

Accurate counts of wildlife deaths in spills are always difficult because stricken animals frequently crawl away to die or sink to the bottom of a water body, while others make easy targets for predators, said Melanie Driscoll, the National Audubon Society’s director of bird conservation for the Gulf Coast.

To compensate for those factors, spill specialists use multipliers supplied by computer models.

“A body count in these spills is just that — a count of the carcasses that were found, not an accurate picture of how many were really killed.” — Melanie DriscollIn the Exxon Valdez event — a smaller spill in a smaller area than the Deepwater Horizon — scientists put the number of dead birds at 225,000, a figure arrived at after applying multipliers ranging from 10 to 30 to the total number carcasses of various species that were actually recovered.

“In some cases the multiplier can be 12 or 5 or even 20,” said Driscoll. “I’ve seen a number as high as 50 by one group for dolphins and whales in this spill. So that would mean if 20 dead dolphins were collected, you multiply that number by 50, and you get 1,000 – which would be much closer to the actual damage done.

“In this spill I would expect the multipliers for birds to be huge.”

That’s because recovery operations during the Deepwater Horizon disaster faced additional complications. The spill occurred at the beginning of the five-month nesting season for pelicans and other birds, and it covered a much larger area than the Exxon Valdez — 68,000 square miles compared to 11,000.

“The decision was made not try to recover dead birds from the nesting islands to avoid causing even more deaths,” said Driscoll. “That meant most of those sites were not searched until late August or early September at the earliest” — months after the disaster struck, in April.

The delay meant adult pelicans, their eggs and then their young were being contaminated as long as BP’s oil was in Barataria Bay. Plastic and cloth booms placed around the islands to collect the oil provided only marginal protection because the pelicans’ daily food searches took them into the oil-fouled waters beyond the booms.

Less fortunate adults were completely soaked in oil, and the heart-breaking photos of their struggles soon became iconic images of the disaster.

Pairs returning to their nests with oil on their feathers smeared the toxic substance on porous eggs they were incubating. And when the surviving young were old enough, they walked and swam through the weathered oil around the booms.

Driscoll said by the time search teams entered the islands, many birds that had died from oil contamination likely had decomposed or had been eaten by scavengers. Nor could there ever be an accurate count of the eggs that failed to hatch due to the oil.

She said the real toll on all birds in the northern Gulf could reach six figures because the delay in counting could mean “thousands, tens of thousands, maybe hundreds of thousands of carcasses just disappeared.”

The location of this spill would only add to the multiplier, she said. In the sub-tropical Gulf, predation takes place 24/7, 365, which means anything of food value doesn’t last long.

“It’s an incredibly productive system so that means there is also an incredible number of predators,” Driscoll said. “And this was spread over a really huge area, which complicated the collection as well.”

The difficulty of coming up with an accurate number has been compounded by the paucity of post-spill research on birds in the impacted area, Driscoll said.

“Of the $500 million BP set aside for research on Deepwater Horizon impacts, dozens and dozens of studies have been done on oysters and fish, and I know of just two that have been started on birds,” she said.

“I understand the studies on oysters and fish; everybody needs to know what’s happening in the food chain. But we are four years removed from the spill, and we don’t have answers to questions like what the long-term impacts could be.”

Research by government agencies as part of the Natural Resource Damage Assessment has been kept from the public. That’s because monetizing the damage done to fish, wildlife and habitat plays out like a personal-injury lawsuit, with opposing sides reluctant to tip off the other to their findings.

One study in Minnesota on the breeding success of white pelicans, winter residents of coastal Louisiana, is a cause for concern. October arrivals in Gulf waters, the whites would have missed most of the surface oil, but they spent the next six months feeding on fish in bays polluted by the disaster. The researchers collected 200 eggs that didn’t hatch and looked for evidence of oil contamination.

“The study is still under way, but of the first 30 un-hatched eggs they looked at, 90 percent had the chemical signature of Deepwater Horizon oil,” Driscoll said, “and 80 percent had the signature of the dispersant Corexit, which was widely used during the spill.

“Now there may have been other reasons why these eggs didn’t hatch. But what they found is significant — and it’s the kind of research we should be doing on many other species here in the Gulf, but we aren’t.”

One clue to the long-term impact of the spill on Louisiana brown pelicans could arrive this summer as many of the birds born during the disaster enter their first spawning season.

“Pelicans got a lot of attention, and deservedly so, but the reality is their populations have been doing quite well with all the help they’ve received from humans over the last 40 years,” she said.

“They have a fairly large population with as many as 70,000 to 80,000 in Louisiana alone, and many more in other states. But there are only 6,000 Wilson’s plovers in the entire Gulf, so losing even a small number of that species could be a real problem.”

In fact, the official list of birds killed by the spill shows only two Wilson’s plover carcasses collected. But that doesn’t assure Driscoll that the plover population escaped major damage.

“A body count in these spills is just that — a count of the carcasses that were found, not an accurate picture of how many were really killed,” said Driscoll. “What’s been so frustrating in our community is the lack of information.

From 2013 to 2017, Bob Marshall covered environmental issues for The Lens, with a special focus on coastal restoration and wetlands. While at The Times-Picayune, his work chronicling the people, stories and issues of Louisiana’s wetlands was recognized with two Pulitzer Prizes and other awards. In 2012 Marshall was a member of the inaugural class inducted into the Loyola University School of Communications Den of Distinction.